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tions of the things intended. Give them to a person who did not previously know how to distinguish between solidity and fluidity, and he might certainly be led to doubt whether an oak tree was a solid, or whether sand, dough, and sponge, were not fluids.
The motion of a body falling freely to the ground, belongs to Dynamics: the motion of the same body descending on an inclined plane, belongs to Mechanics.'
According to the principle on which this distinction is founded, the curve of quickest descent, and the precession of the equinoxes, belong to mechanics, rather than to dynamics. This is passing strange.'
In reasoning upon the first law of motion, Mr. Playfair first shows that a moving body left to itself will not change its direction; and then proceeds thus:
Lastly, it cannot change its velocity; for if its velocity change, that change must be according to some function of the time; so that if C be the velocity which the body has at any instant, and t the time counted from that instant, V the velocity at the end of the time t, the relation between V, C, and t, must be expressed thus, V = C + A tm + B th + &c. Now there is no condition involved in the nature of the case, by which the coefficients A, B, &c. can be determined to be of any one magnitude rather than of any other; each of them is therefore equal to O, and the equation is VC, so that the velocity remains constant.'
We object to this, 1st, because it is unnecessary; 2d, because it is unsatisfactory. Unnecessary, because both change of direction and change of velocity being changes of state, cannot be even imagined to take place without a cause; and therefore the proposition is admissible independent of the Professor's refined reasoning. Unsatisfactory, because many other things, whether doubtful or not, may be proved by the same process, without the alteration of a single word. Let it be affirmed, for instance, that the suns of this and of all other systems, move round our moon, or any other satellite, as a centre of force; and let it be farther asserted that in such case, the motion of Sirius (or any other fixed star) is uniform; the assertor, in order to establish his proposition, has only to say, 'it cannot change its velocity,' and, following the Professor verbatim through the above quotation, he will accomplish his object; though the thing thus proved is one of the most improbable things in nature.
Our author treats of Archimedes' screw, under the head of mechanics; yet we cannot help doubting whether it would not have fallen better among the discussions respecting Hydraulics; especi ally as it is a machine for raising water.
Mr. Playfair too, like some other philosophers of the present day, seems fond of a reference to ideal laws, such as the law of
continuity, aud that of the sufficient reason.' In speaking of the former of these, he does not plead for its universality, because he has found one case, namely, that of friction, (p. 90,) which violates' the law; but he evinces a strong partiality for it. Thus, after exhibiting what he calls the fundamental equation of Dynamics, i. e. Ft, he adds the above is called the LAW OF CONTINUITY, which, in what respects free motions, is never violated.' And again, speaking of the radiation of heat, he says a body heated, though not so as to shine, and placed before a concave speculum of metal, communicates heat instantaneously to a thermometer in the corresponding focus. A cold body does the same, and it is remarkable that an effect so difficult to be explained, is, nevertheless, perfectly consistent with the law of continuity.'
This appears to us little better than trifling. Let continuity be admitted as a fact of frequent, and indeed daily and hourly occurrence, and all would be very well; but why should it usurp the name and the place of a law? of a law of nature, we mean, for such it is, or no law at all. Now, it cannot be a law of nature, for it is often violated where there is no miracle. It is as much violated in every change from quiescence to motion, as in the creation of a world; and in extinguishing the flame of a candle, any person may conceive a hundred ways in which there shall be a complete rupture of continuity in the passage from light to darkness. Nor, indeed, can this be an invariable law of analytical formula, though the Professor considers it in this light, (if we rightly understand him) at p. 49. We may adduce an instance even from the theory of dynamics, in which the law' fails. Supposing an atom of gravitating matter represented by a mathematical point to be attracted by a spherical surface, considered as consisting of similar matter: the point will be attracted by a force which varies inversely as the square of the distance from the centre of the sphere, as long as this distance remains greater than the radius of the sphere; but when it becomes equal to the radius, the force changes abruptly to one half, and the instant that it becomes less than the radius, it vanishes altogether.
Thus much for the law of continuity;' let us now be indulged with a few words respecting the principle of the sufficient reason.'
'Two things of which the conditions are determined by reasons that are precisely the same, are in all respects similar to one another. Hence, also, if there are two conditions, and no reason to determine a subject to be in one of them rather than another, we are to conclude that it is in neither. This axiom has been called the principle of the SUFFICIENT REASON. It may be used to great advantage for demonstrating the more simple propositions of geometry, as well as of mechanics.'
Such is Professor Playfair's statement of this principle. By way of application he says, 'two events which are determined by circumstances precisely the same, are conceived to happen in equal portions of time.' Now, on this proposition it is obvious to remark, that it need not be conceived at all, unless the circumstances are the same in point of time; and then all the other circumstances may be excluded, and the proposition will amount to saying that events which happen in equal times will happen in equal times. Hence, instead of affirming with the Professor, that it is on the principle of the sufficient reason that time is divided into equal portions; we would say that there is sufficient reason for so dividing time, without any reference to this much admired principle. In truth, it is not a little singular that so ridiculous a vagary should ever have been classed among philosophical opinions.
In the two particulars just noticed, the learned professor, if he errs, as we conceive he does, errs in company: but in most of the remaining points which we mean to touch upon, he either stands or falls alone.
'The great advantage (says he) which Natural Philosophy seems to possess exclusively, arises from this, that the action which it treats of, extends to large masses of matter, and to considerable distances, such as can be measured by lines and numbers.'
How does this apply to various cases of Galvanic action? Or is not Galvanism a branch of natural philosophy?
All bodies have empty spaces disseminated through them in the form of pores more or less minute.'
Have pores, then, a distinct or peculiar form?
"From the porosity of bodies, it follows, that the particles of matter can only touch one another in a few points.'
This does not follow at all, as a necessary consequence from porosity, merely; nor from any thing which has been discovered of porosity generally. Cubes or parallelepipeds might be so placed as to have vacuities, almost as large as between spheres in contact, and yet touch at nearly half their respective faces.
Magnetism is a permanent quality; it is peculiar to iron and its
Here, the former part of the sentence is ambiguous, the latter erroneous. If permanence mean, as it frequently does, continuance in the same state,' it does not apply to the magnetic force, which is considerably liable to intension and remission, as when
VOL. VIII. NO. XV.
exposed to heat and cold. Nor is this quality peculiar to iron and its ores; for it exists in pure nickel almost in an equal degree.
Of the second law of motion, Mr. Playfair says, when expressed more precisely, it involves two distinct propositions.'These he enunciates, and then remarks, the first of these propositions involves in it the first law of motion.' If this be correct, that is, if this involve the first law of motion, and the second law involves this, it will follow, we apprehend, that the second law involves the first, and, of course, that the first is superfluous. Indeed the Professor admits this expressly, for he refers the inertia of body to both. In this respect he deviates from all authority. Even the French authors, who seem extremely well disposed to abolish these axioms from mechanical science, refer this property to the first. Carnot, for example, speaking of it under the name of la première hypothèse,' says, Cette hypothèse est le principe connu sous le nom de loi d'inertie; et on l'exprime ordinairement, en disant que tout corps persévère dans son état de repos ou de mouvement uniforme et rectiligne, jusqu'à ce qu'il recoive l'action d'une puissance étrangère.'
How Mr. Playfair wishes to dispose of the third law, we have not been able to discover, as he does not mention it at all. But as far as we can manage to unravel his sentiments from these Outlines,' it would seem that he thinks the whole of mechanical science may be made to rest upon the single principle, that the action and reaction of bodies on one another are equal.'
We might proceed to remark upon the Professor's loose definition of impenetrability, his fields of vacuity,' his' elastic fluid circumfused about a solid,' (by which we conjecture he means the atmosphere surrounding the earth,) and a few more such peculiarities; but we have only room to advert to his inaccuracy respecting motion. With respect to the continuity of motion, the Professor employs an argument, at page 50, which, if pushed a little farther, would go to the denial of motion altogether. And again, as the action of bodies on one another generally involves motion, the consideration of that power constitutes one of the main objects of natural philosophy.' Thus, since motion is a power, it follows, according to the Professor, that change of place is a power: and farther, since he tells us that power is known to us only as the cause of motion, and measured by the motion it produces,' and in another place, that the cause of motion is denominated force,' it follows that force is the cause of power, nay, that power is 'the cause, of power, and is measured by the power which it produces!'
Several of these, we are aware, may be contemplated as merely verbal inaccuracies. But verbal inaccuracies in philosophical definitions and propositions are serious things. In mathematics
and natural philosophy, the simple omission or change of a word, may completely change the face of a proposition, and cause it either to communicate a wrong idea, or no idea at all. Take, for example, the geometrical truth, if more than two equal right lines can be drawn from any point within a circle to the circumference, that point is the centre; and it is manifest, that if either the words equal, right, or to the circumference, be omitted, the theorem is no longer true. In like manner, when a lecturer affirms that a fact is a hypothesis, that empty spaces are in the form of pores; that motion is a power; that it is on the principle of the sufficient reason that time is divided into equal portions, &c. and describes a fluid so that it will comprehend sand, flour, or almost any other loose aggregation of small particles, his language is defective in philosophical precision, tends to mislead, and is therefore worse than useless. Besides, in a work like the present, in which there are not ten pages, probably, of direct and new analytical investigation, verbal errors are the only ones that can reasonably be looked for. Professor Playfair has been too long accustomed to the management of algebraical expressions, to blunder much in that way, even if he filled a volume with them.
ART. X. The Life and Administration of Cardinal Wolsey. By John Galt. 4to. Cadell. 1812.
THE association of ideas, between local appearances and distant events, has not unfrequently called forth the latent powers of intellect, and become the parent of great undertakings in literature, as well as in active life: this species of inspiration appears to have been felt by the author of the present work, who sets out with assuring his readers, that it was suggested to him several years ago, while standing in the great quadrangle of Christ Church College, Oxford.'
There must be something very capricious in the rules by which this spirit makes choice of its recipients, when we find that neither taste nor talent, neither constant residence in that illustrious seminary, intimate connection with its interests, nor personal gratitude to its founder, should have struck out that spark in the genuine sons of Christ Church, which unaccountably lighted on a stranger not eminently gifted for the purpose, in consequence of accidentally standing on the spot which Wolsey's munificence had devoted to literature;-that a life omitted or unthought of by Fell, and Atterbury, and Aldrich, who, while they ate the bread,